1. Technical Field
This invention relates to the field of superhard materials and allotropic forms of carbon, and more particularly to a new phase of carbon embodying a new crystal structure comprised of three-fold coordinated carbon only.
2. Discussion of the Prior Art
Superhard materials refers to solids of hardness comparable to or in excess of that of diamond Examples are diamond itself, cubic boron nitride (C-BN, tradename: borazon), boron suboxides (B.sub.22 O), and a new (possibly hypothetical) compound C.sub.3 N.sub.4. The extreme hardness of such materials is exploited in high-speed cutting and grinding tools and low-friction, long-wearing bearing surfaces. Recent advances in chemical vapor deposition (CVD) of such materials in thin film form has broadened the application of superhard materials as surface coatings. However, materials even harder than diamond have been avidly sought with unsatisfactory results This invention has discovered a new crystalline form of carbon which is harder than diamond, less dense than diamond, is metallic, and characterized by three-fold atomic coordination (sp.sup.2 bonding) only.
The only mention in the prior art of which applicants are aware that a carbon Phase harder than diamond has been made appears in articles by N.N. Matyusenko and V.E. Strel'nitskii, in Journal of Experimental and Theoretical Physics Letter, Vol. 30, page 199 (1979); and by A.S. Bakai and V.E. Strel'nitskii, in Annals of Technical Physics. Vol. 51, page 2414 (1981). Such articles purport to describe the process of formation and properties of a "super-dense" form of carbon which is both harder and denser than carbon. The existence of this new carbon phase, called C-8 or "supercubane" is a subject of dispute in the technical community because of its extreme difficulty to make and isolate. C-8 carbon consists of four-fold coordinated (sp.sup.3 bonded) carbon in a highly distorted configuration and, disadvantageously, will require high pressure processing.
Other investigators have speculated that other allotropic forms of carbon may exist, but this invention has established and teaches how to make a new allotropic form of carbon which is consists of sp.sup.2 coordinated carbon only, is metallic, is harder than diamond, but less dense, and has a higher bulk modulus than diamond.